Lyocell fiber

ABSTRACT

This invention relates to a lyocell fiber and, more specifically, to a lyocell fiber exhibiting the same or improved physical properties even if used in a lesser amount, compared to a conventional lyocell fiber, by controlling the shape of the section of a monofilament included in the lyocell fiber to increase the specific surface area of the fiber.

TECHNICAL FIELD

The present invention relates to a lyocell fiber.

BACKGROUND ART

A fiber is a piece of natural or synthetic linear material that isflexible and thin and has a high ratio of length to thickness. Fibersare classified into long fibers, semi-long fibers, and staple fibersaccording to the type thereof, and into natural fibers and syntheticfibers according to the raw material thereof.

Fibers have had a close relationship with human life since old times,and natural fibers such as cotton, linen, wool, and silk have long beenused as the main raw material for clothes. The use of fibers hasextended beyond a material for clothes to industrial materials inaccordance with the advancement of science and technology since theindustrial revolution. In order to meet the rapidly growing demand forfibers due to cultural development and the increase in population,synthetic fibers have been developed as novel fiber materials.

Among synthetic fibers, regenerated fibers have an excellent tactile andwearing sensation and a very fast water-absorbing and dischargingability, compared to cotton, thus being frequently used as the rawmaterial of clothes. In particular, rayon fibers, among regeneratedfibers, have excellent gloss and color development and realize the sametactile sensation as natural fibers. Rayon fibers are considered to be amaterial that is harmless to the human body, and accordingly, have beenused extensively in the past. However, rayon fibers easily shrink andwrinkle, the manufacturing process thereof is complicated, and a lot ofchemicals are used during a process for melting wood pulp, which causesenvironmental pollution in work and during wastewater treatment.

Accordingly, a study has been made to find fibers that are not harmfulto the environment and the human body and have excellent physicalproperties compared to other fibers. Recently, lyocell fibersmanufactured using natural pulp and amine oxide hydrate have beenproposed. Lyocell fibers have excellent physical fiber properties suchas tensile strength and tactile sensation, compared to conventionalregenerated fibers, and do not cause any contamination during theproduction process thereof, an amine oxide-based solvent used to formthe lyocell fibers may be recycled, and the lyocell fibers arebiodegradable when use thereof has been completed. Accordingly, lyocellfibers have been used as environment-friendly fibers in various fields.

However, current lyocell fibers can be produced only in the form ofproducts having a circular section. Since it is expected that lyocellfibers may be imparted with various physical properties depending on thesectional shape thereof, there is a demand for a technology formanufacturing lyocell fibers having various types of sections.

DISCLOSURE Technical Problem

Accordingly, the present invention has been made keeping in mind theabove problems occurring in the related art, and an object of thepresent invention is to provide a lyocell fiber having a large specificsurface area.

Technical Solution

In order to accomplish the above object, the present invention providesa lyocell fiber including a lyocell multifilament manufactured byspinning a lyocell spinning dope including a cellulose pulp and anN-methylmorpholine-N-oxide (NMMO) aqueous solution. The multifilamentincludes a monofilament having a multi-lobal section, the multi-lobalsection includes a plurality of projections, and the plurality ofprojections comes into contact with a first virtual circle and a secondvirtual circle, included in the first virtual circle, is integrallyformed with the second virtual circle serving as a core, and comes intocontact with the first virtual circle at ends thereof.

The lyocell spinning dope may include 6 to 16 wt % of the cellulose pulpand 84 to 94 wt % of the N-methylmorpholine-N-oxide aqueous solution.

The cellulose pulp may have an alpha-cellulose content of 85 to 97 wt %and a degree of polymerization (DPw) of 600 to 1700.

In the lyocell fiber, a space occupancy ratio defined in the followingEquation 1 may be 150 to 400%.

Space occupancy ratio (%)=(Area of first virtual circle/sectional areaof monofilament included in lyocell fiber)×100  <Equation 1>

The first virtual circle may have a radius of 8 to 30 μm.

The second virtual circle may have a radius of 3 to 12 μm.

Advantageous Effects

According to the present invention, a lyocell fiber having a largespecific surface area is provided in a manner capable of exhibiting thesame or improved physical properties even if used in a lesser amount,compared to a conventional lyocell fiber, when the lyocell fiber isapplied to reinforcing materials in the clothing, construction, andvehicle fields.

DESCRIPTION OF DRAWINGS

FIG. 1 shows a section of a monofilament included in a lyocell fiberaccording to an embodiment of the present invention; and

FIGS. 2a to 2c show the sections of lyocell fibers manufactured inExamples of the present invention, and FIGS. 2a, 2b, and 2c are picturesshowing the sections of the lyocell fibers manufactured in Examples 1,2, and 3, respectively.

DESCRIPTION OF THE REFERENCE NUMERALS IN THE DRAWINGS

-   -   1: Core, 2: Projection, 3: Long axis of projection,    -   4: Recess of projection, 5: End of projection,    -   11: First virtual circle, 12: Second virtual circle

BEST MODE

Hereinafter, the present invention will be described in greater detail.

The present invention relates to a lyocell fiber including a lyocellmultifilament manufactured by spinning a lyocell spinning dope includinga cellulose pulp and an N-methylmorpholine-N-oxide (NMMO) aqueoussolution. The multifilament includes a monofilament having a multi-lobalsection, and the multi-lobal section includes a plurality ofprojections. The plurality of projections comes into contact with afirst virtual circle and a second virtual circle, included in the firstvirtual circle, is integrally formed with the second virtual circle,which serves as a core, and comes into contact with the first virtualcircle at ends thereof.

[Multi-Lobal Section]

In the present invention, a multi-lobal section is a section including aplurality of projections. Specifically, as shown in FIG. 1, themulti-lobal section is a section including one core 1 and a plurality ofprojections formed around the core so as to be integrated with the core.

Specifically, the size and the shape of the multi-lobal section may bedefined within the boundary of a first virtual circle 11 connecting theends of the plurality of projections, and the boundary of a secondvirtual circle 12 included in the first virtual circle 11. The radius ofthe first virtual circle 11 is larger than that of the second virtualcircle 12, and the first virtual circle 11 and the second virtual circle12 may be preferably concentric. However, the first virtual circle 11and the second virtual circle 12 may not be concentric.

The multi-lobal section includes the plurality of projections. Theplurality of projections is integrally formed with the core 1overlapping the second virtual circle 12, ends 5 of the projections comeinto contact with the first virtual circle 11, and a recess 4 formedbetween the projections comes into contact with the second virtualcircle 12.

In the present invention, the multi-lobal section may include threeprojections in order to maximize the specific surface area of thelyocell fiber.

The first virtual circle and the second virtual circle may have radii of8 to 30 μm and 3 to 12 μm, respectively.

When the radius of the first virtual circle is 8 μm or more, themulti-lobal section may be embodied, and when the radius is 30 μm orless, a monofilament having a denier suitable as that of fiber productsmay be formed. Further, when the radius of the second virtual circle is3 μm or more, the multi-lobal section may be embodied, and when theradius is 12 μm or less, a monofilament having a denier suitable as thatof fiber products may be formed.

The monofilament included in the lyocell fiber according to the presentinvention may have the aforementioned multi-lobal section, and in thelyocell fiber, a space occupancy ratio, defined in the followingEquation 1, may be 150 to 400%.

Space occupancy ratio (%)=(Area of first virtual circle/sectional areaof monofilament included in lyocell fiber)×100  <Equation 1>

The space occupancy ratio means the ratio of the substantial occupancyspace of the monofilament in the fiber, depending on the projections ofthe multi-lobal section. That is, when the monofilament included in thelyocell fiber has a circular section, since the sectional area of themonofilament is the same as the area of the first virtual circle, thespace occupancy ratio, defined above, becomes 100%. However, in the caseof the fiber having the multi-lobal section including the projections,the actual occupancy area of the fiber is increased due to theprojections. Therefore, it can be seen that the specific surface area ofthe fiber is increased as the space occupancy ratio is increased.

The lyocell fiber of the present invention has excellent properties suchas swelling, interface adhesion, and quick drying due to an increase inspecific surface area, and has a space occupancy ratio, defined inEquation 1, of 150 to 400%, and preferably 300 to 400%.

Meanwhile, the present invention relates to a method of manufacturing alyocell fiber. The method includes (S1) spinning a lyocell spinning dopeincluding a cellulose pulp and an N-methylmorpholine-N-oxide (NMMO)aqueous solution, (S2) solidifying the lyocell spinning dope, spunduring the step (S1), to obtain a lyocell multifilament, (S3) washingthe lyocell multifilament obtained during the step (S2), and (S4)treating the lyocell multifilament, washed during the step (S3), usingan emulsion. The multifilament includes a monofilament having amulti-lobal section, the multi-lobal section includes a plurality ofprojections, and the plurality of projections comes into contact withboth a first virtual circle and a second virtual circle included in thefirst virtual circle, is integrally formed with the second virtualcircle, which serves as a core, and comes into contact with the firstvirtual circle at ends thereof.

[Step (S1)]

During the step (S1), the lyocell spinning dope including the cellulosepulp and the N-methylmorpholine-N-oxide (NMMO) aqueous solution is spun.

The lyocell spinning dope may include 6 to 16 wt % of the cellulose pulpand 84 to 94 wt % of the N-methylmorpholine-N-oxide aqueous solution.The cellulose pulp may have an alpha-cellulose content of 85 to 97 wt %and a degree of polymerization (DPw) of 600 to 1700.

When the content of the cellulose pulp in the lyocell spinning dope isless than 6 wt %, it may be difficult to ensure fibrous characteristics,and when the content is more than 16 wt %, it may be difficult todissolve the pulp in the aqueous solution.

Further, when the content of the N-methylmorpholine-N-oxide aqueoussolution in the lyocell spinning dope is less than 84 wt %, thedissolution viscosity may be significantly increased, which isundesirable. When the content is more than 94 wt %, the spinningviscosity may be significantly reduced, making it difficult to ensureuniform fibers during the spinning step.

The weight ratio of N-methylmorpholine-N-oxide and water may be 93:7 to85:15 in the N-methylmorpholine-N-oxide aqueous solution. When theweight ratio of N-methylmorpholine-N-oxide is more than 93(%), thedissolution temperature may be increased, thus decomposing celluloseduring the dissolution of the cellulose. When weight ratio ofN-methylmorpholine-N-oxide is less than 85(%), the dissolutioncapability of the solvent may be reduced, making it difficult todissolve cellulose.

The spinning dope is discharged through the spinning nozzle of aspinneret. The spinning dope on the filament is discharged through theair gap section of the spinneret into a solidifying solution in asolidifying bath. The spinning dope may be discharged from the spinneretat a spinning temperature of 80 to 130° C.

The spinneret may have a plurality of unit holes when one unit hole isset to include a plurality of holes. The number of holes included in theunit hole may be the same as the number of projections of themulti-lobal section. For example, the number of holes included in theunit hole may be three in order to manufacture a lyocell fiber thatincludes a monofilament having a multi-lobal section including threeprojections.

[Step (S2)]

During the step (S2), the lyocell spinning dope, spun during the step(S1), is solidified to obtain the lyocell multifilament. Thesolidification of the step (S2) may include a primary solidifying stepof supplying cooled air to the spinning dope to solidify the spinningdope using air quenching (Q/A) and a secondary solidifying step ofadding the primarily solidified spinning dope to the solidifyingsolution to solidify the spinning dope.

During the (S1) step, the spinning dope may be discharged through thespinneret and then pass through the air gap section between thespinneret and the solidifying bath. Cooled air is supplied from adonut-shaped air cooler, positioned in the spinneret, to the air gapsection in the outward direction from the inside of the spinneret.Cooled air may be supplied to the spinning dope to primarily solidifythe spinning dope using air quenching.

Factors affecting the physical properties of the lyocell multifilamentobtained during the step (S2) are the temperature and the wind speed ofcooled air in the air gap section. Cooled air may be supplied to thespinning dope at a temperature of 4 to 15° C. and a wind speed of 5 to50 m/s to thus solidify the spinning dope during the step (S2).

When the temperature of cooled air is lower than 4° C. during primarysolidification, the surface of the spinneret is cooled, the sections ofthe lyocell multifilaments become nonuniform, and spinningprocessability is reduced. When the temperature is higher than 15° C.,primary solidification using cooled air is insufficiently performed,reducing spinning processability.

Further, when the wind speed of cooled air is less than 5 m/s duringprimary solidification, primary solidification using cooled air isinsufficiently performed, reducing the spinning processability causingyarn breakage. When the wind speed is more than 50 m/s, spinning dope isdischarged from the spinneret while being shaken due to the air, thusreducing spinning processability.

After primary solidification using air quenching, the spinning dope maybe supplied to the solidifying bath containing the solidifying solutionto thus perform secondary solidification. Meanwhile, the temperature ofthe solidifying solution may be 30° C. or less in order to performappropriate secondary solidification. With regard to this, since thesecondary solidification temperature is not unnecessarily high, anappropriate solidifying speed is maintained. The solidifying solutionmay be manufactured so as to have a typical composition in the art towhich the present invention belongs, and accordingly, the solidifyingsolution is not particularly limited.

[Step (S3)]

During the step (S3), the lyocell multifilament obtained during the step(S2) is washed.

Specifically, the lyocell multifilament obtained during the step (S2)may be transported to a pulling roller and then to a washing bath tothus be washed.

When the filament is washed, in consideration of ease of recovery andreuse of a solvent after washing, a washing solution having atemperature of 0 to 100° C. may be used, and water may be used as thewashing solution, and other additive components may be further includedif necessary.

[Step (S4)]

During the step (S4), the lyocell multifilament washed during the step(S3) may be treated using an emulsion and then dried.

For treatment using the emulsion, the multifilament is completelyimmersed in the emulsion to be coated, and the amount of the emulsionapplied on the filament is maintained using squeezing rollers attachedto a feeding roll and a discharging roll of an emulsion-treatmentapparatus. The emulsion serves to reduce friction caused when thefilament comes into contact with a drying roller and a guide during acrimping step.

The lyocell fiber is biodegradable and thus environmentally friendly.

Further, in the lyocell fiber, since the monofilament has a multi-lobalsection including a plurality of projections, the specific surface areathereof is increased. Accordingly, the manufactured lyocell fiber mayexhibit the same or improved physical properties even if used in alesser amount, compared to a conventional lyocell fiber having acircular section.

Particularly, the lyocell fiber according to the present invention has alarge specific surface area, which exhibits the same or improvedphysical properties, compared to a conventional lyocell fiber, even ifused in a lesser amount when the lyocell fiber is applied as areinforcing material in the clothing, construction, and vehicle fields.

When the lyocell fiber according to the present invention is used forclothes, the lyocell fiber exhibits excellent properties such ashygroscopicity and quick drying due to the large specific surface areathereof. Accordingly, the lyocell fiber does not cling to the body, evena sweaty body, thereby always providing a pleasant state to the skin tothus reduce discomfort. Further, the lyocell fiber helps to quickly andcontinuously dry sweat. Specific examples of application of the lyocellfiber for use in clothes may include outdoor wear, sportswear, t-shirts,golf wear, men's and women's clothing, functional underwear, hats,sports socks, and underwear.

When the lyocell fiber according to the present invention is used as areinforcing material, a reinforcing ability is increased as a contactarea between the lyocell fiber and materials to be reinforced isincreased. The lyocell fiber may be applied to MRG (mechanical rubbergoods), such as tire cords and hose reinforcing materials, cementreinforcing materials, and interior materials of vehicles.

MODE FOR INVENTION

A better understanding of the present invention may be obtained throughthe following Examples. It will be apparent to those skilled in the artthat the following Examples are intended to illustrate the presentinvention but are not to be construed to limit the scope of the presentinvention.

Example 1

Cellulose pulp having a degree of polymerization (DPw) of 820 and analpha-cellulose content of 93.9% was mixed with an NMMO/H₂O mixturesolvent (a weight ratio 90/10) having a propyl gallate content of 0.01wt % to manufacture 12 wt % of a spinning dope for use in a lyocellfiber.

The spinning dope was maintained at a spinning temperature of 110° C. ina spinning nozzle of a spinneret having a plurality of unit holes eachincluding three holes. The spinning dope was spun while the dischargeamount and the spinning speed of the spinning dope were controlled sothat the monodenier of the filament was 3.37 denier. The spinning dope,discharged from the spinning nozzle, on the filament was suppliedthrough an air gap section to a solidifying solution in a solidifyingbath. The spinning dope was primarily solidified in the air gap sectionusing cooled air at a temperature of 8° C. and a wind speed of 10 m/s.

The solidifying solution included 85 wt % of water and 15 wt % of NMMOat 25° C.

The concentration of the solidifying solution was continuously monitoredusing a sensor and a refractometer.

The filament elongated in an air layer using a pulling roller was washedusing a sprayed washing solution in a washing apparatus to removeremaining NMMO. After an emulsion was uniformly applied on the filament,the resultant filament was squeezed so that the content of the emulsionin the filament was maintained at 0.2%, and dried using a drying rollerat 150° C. to manufacture a lyocell fiber including a multifilament. Themultifilament included a monofilament having a multi-lobal sectionincluding three projections.

Example 2

The same procedure as Example 1 was repeated to manufacture a lyocellfiber, which included a multifilament including a monofilament having amulti-lobal section including three projections, except that themonodenier of the filament was 3.58 denier.

Example 3

The same procedure as Example 1 was repeated to manufacture a lyocellfiber, which included a multifilament including a monofilament having amulti-lobal section including three projections, except that themonodenier of the filament was 14.82 denier.

Comparative Example 1

The same procedure as Example 1 was repeated to manufacture a lyocellfiber, which included a multifilament including a monofilament having acircular section, except that the spinneret that was used had aplurality of unit holes each including one hole having a circularsection, and that the monodenier of the filament was 1.73 denier.

Comparative Example 2

The same procedure as Comparative Example 1 was repeated to manufacturea lyocell fiber, which included a multifilament including a monofilamenthaving a circular section, except that the monodenier of the filamentwas 2.97 denier.

The shape of the section, the denier, and the space occupancy ratio ofthe monofilament that was included in the lyocell fiber manufactured inthe Examples and the Comparative Examples were measured and calculatedusing the following methods, and the results are set forth in thefollowing Table 1.

(1) Sectional Shape of the Monofilament Included in the Lyocell Fiber

A few bundles of fibers were sampled and then rolled together with blackcotton. The resultant fiber was processed to be thin and then insertedinto a hole in a plate that was used to transversely cut the fiber.Subsequently, the fiber was cut using a razor blade in a way such thatthe shape of the section thereof was not changed.

The cut section of the fiber was magnified (×200) and observed using anoptical microscope (BX51, products manufactured by Olympus Corporation),and the image of the section was stored using a digital camera. Thedesired section was selected and the radius and the area of the sectionwere analyzed using an image of the section of the fiber according tothe Olympus soft imaging solution program.

(2) Denier

The denier of the lyocell fiber was calculated from the sectional areaof the monofilament of the real lyocell fiber, which was obtained fromthe section analysis, and the density of the lyocell fiber using thefollowing Equation 2.

Density of lyocell fiber=1.49 g/cm³

Denier (De)=[Sectional area of monofilament of lyocell fiber(μm²)×Density of lyocell fiber (g/cm³)×9000 (m)]/1000000  <Equation 2>

(3) Space Occupancy Ratio

The space occupancy ratio of the lyocell fiber was calculated using thefollowing Equation 1.

Space occupancy ratio (%)=(Area of first virtual circle/sectional areaof monofilament included in lyocell fiber)×100  <Equation 1>

TABLE 1 Shape of section of monofilament included in lyocell fiberRadius Radius Sectional of of area of first second Area of mono- Spacevirtual virtual first filament occu- circle circle virtual of actualpancy (L1, (L2, circle lyocell Denier L1/L ratio μm) μm) (μm²) fiber(μm²) (De) 2 (%) Example 1 16.75 3.87 881 251.6 3.37 4.33 350 Example 211.44 6.16 411 266.6 3.58 1.86 154 Example 3 27.78 11.61 2423 1105 14.822.40 219 Com- 6.4 6.4 129 129 1.73 1 100 parative Exam- ple 1 Com- 8.48.4 222 222 2.97 1 100 parative Exam- ple 2

As shown in Table 1, the lyocell fiber including the monofilament havingthe multi-lobal section of Examples 1 to 3 exhibited a space occupancyratio larger than that of the lyocell fiber including the monofilamenthaving the circular section of Comparative Examples 1 and 2. The sectionof the lyocell fiber of Examples 1 to 3 is shown in FIGS. 2a to 2 c.

INDUSTRIAL APPLICABILITY

From the aforementioned results, it can be seen that the lyocell fiberof Examples 1 to 3 has a large specific surface area and may beextensively applied in fields requiring a fiber having a large specificsurface area.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

1. A lyocell fiber comprising: a lyocell multifilament manufactured byspinning a lyocell spinning dope including a cellulose pulp and anN-methylmorpholine-N-oxide (NMMO) aqueous solution, wherein themultifilament includes a monofilament having a multi-lobal section, themulti-lobal section includes a plurality of projections, and theplurality of projections comes into contact with a first virtual circleand a second virtual circle, included in the first virtual circle, isintegrally formed with the second virtual circle, serving as a core, andcomes into contact with the first virtual circle at ends thereof.
 2. Thelyocell fiber of claim 1, wherein the lyocell spinning dope includes 6to 16 wt % of the cellulose pulp and 84 to 94 wt % of theN-methylmorpholine-N-oxide aqueous solution.
 3. The lyocell fiber ofclaim 2, wherein the cellulose pulp has an alpha-cellulose content of 85to 97 wt % and a degree of polymerization (DPw) of 600 to
 1700. 4. Thelyocell fiber of claim 1, wherein a space occupancy ratio defined in afollowing Equation 1 is 150 to 400%:Space occupancy ratio (%)=(Area of first virtual circle/sectional areaof monofilament included in lyocell fiber)×100.  <Equation 1>
 5. Thelyocell fiber of claim 1, wherein the first virtual circle has a radiusof 8 to 30 μm.
 6. The lyocell fiber of claim 1, wherein the secondvirtual circle has a radius of 3 to 12 μm.
 7. The lyocell fiber of claim1, wherein the first virtual circle and the second virtual circle areconcentric.